Field of the Invention
The present invention describes a process for preparing N,N-(di)alkylaminoalkyl(meth)acrylamide or N,N-(di)alkylaminoalkyl (meth)acrylate and the quaternary ammonium salts thereof with a low content of the compounds corresponding to the formula (IV).
Description of the Related Art
The preparation of dimethylaminopropylmethacrylamide (DMAPMA) is known from the related art.
EP 0 960 877 (Elf Atochem S.A.) describes a continuous process for preparing methacrylate esters of dialkylamino alcohols. Dialkylamino alcohols are reacted with generally methyl (meth)acrylate, and the dialkylaminoalkyl (meth)acrylate is obtained by the following method:
The mixture of the starting materials (methyl (meth)acrylate and dialkylamino alcohol) is supplied continuously to a stirred reactor together with a tetraalkyl titanate as catalyst (for example tetrabutyl, tetraethyl or tetra(2-ethylhexyl) titanate) and at least one polymerization inhibitor (for example phenothiazine, tert-butylcatechol, hydroquinone monomethyl ether or hydroquinone), where the conversion to the dialkylamino (meth)acrylate is effected at a temperature of 90° C.-120° C. with simultaneous continuous removal of the azeotropic methyl (meth)acrylate/methanol mixture. The crude reaction mixture (crude ester) is fed to a first distillation column, wherein an essentially catalyst-free stream is drawn off at the top of the distillation column under reduced pressure and the catalyst and a little dialkylaminoalkyl (meth)acrylate are drawn off at the bottom of the distillation column. The top stream from the first distillation column is then fed to a second distillation column in which, under reduced pressure, a stream of low-boiling products comprising a little dialkylaminoalkyl (meth)acrylate is drawn off at the top and a stream consisting of mainly dialkylaminoalkyl (meth)acrylate and polymerization inhibitor(s) is drawn off at the bottom and is supplied to a third distillation column. In the third distillation column, under reduced pressure, a rectification is conducted, in which the desired pure dialkylaminoalkyl (meth)acrylate is drawn off at the top and essentially the polymerization inhibitor(s) at the bottom. After further purification with the aid of a film evaporator, the bottom stream from the first distillation column is recycled into the reactor, just like the top stream from the second distillation column.
This process dispenses with dewatering of the alcohols before use, which can lead to increased deactivation of the tetraalkyl titanate used owing to hydrolysis that extends as far as formation of unwanted solid deposits. Furthermore, the process has the disadvantage that the catalyst is subjected to thermal stress at relatively high temperatures in the bottom of the first distillation column. This can easily lead to breakdown of the catalyst.
In this process, there are a total of two overhead rectifications both of the unconverted reactants and of the product. This entails very high energy costs and a total of 4 rectification columns, some of which have to have very large dimensions. The process is therefore afflicted with very high capital and operating costs.
EP 0 968 995 (Mitsubishi Gas Chemical Comp.) describes a continuous process for preparing alkyl (meth)acrylates using a reaction column. The transesterification reaction is effected here directly in a distillation column (i.e. reactor and distillation column for removal of methyl (meth)acrylate/methanol azeotrope form one apparatus), which is supplied continuously with the starting materials (methyl (meth)acrylate and alcohol). The necessary catalyst, here likewise preferably a titanium compound, is present in the distillation column. In the case of a homogeneous catalyst, the catalyst is metered continuously into the distillation column. However, the use of homogeneous catalysts in a distillation column, because of the flushing effect resulting from the liquid reflux in the distillation column, leads to elevated catalyst demand and, in the event of occurrence of solid catalyst precipitation, to soiling of the column internals. In the case of a heterogeneous catalyst, the catalyst is in the reaction column. However, the positioning of the catalyst in the distillation column is disadvantageous because an elevated pressure drop then occurs in the distillation column and, in addition, a very high level of cost and inconvenience is necessary for the regular cleaning of the distillation column. Moreover, heterogeneous catalysts can become deactivated, for example as a result of unwanted polymerization.
U.S. Pat. No. 8,674,133 (Evonik Röhm GmbH) describes a continuous process for preparing alkylamino(meth)acrylamides by means of continuous aminolysis. The reduction in the crosslinker content is achieved here via complex processing steps, especially distillations.
The above-described processes lead to the formation of various by-products, most of which cannot remain in the end product. The removal of the by-products leads to the known disadvantages, for example yield losses and elevated capital, operating and maintenance costs as a result of the purification steps required.